THE CLEODOEA, THE OYSTER, AND THE SCALLOP. 605 



Mr. F. D. Bennett writes as follows : "On that part of the body which 

 is lodged in the apex of the shell there is a small, globular, pellucid 

 body resembling a vesicle, and which at night emits a luminous gleam 

 sufficiently vivid to be visible even when it is opposed to the strong 

 light of a lamp. It is the only example of a luminous shell-fish I have 

 ever met with ; nor would the luminosity of this species be of any avail 

 did not the shell possess a structure so vitreous and transparent. Exam- 

 ples were captured chiefly at night or in the evening." 



The next great group of molluscs is that which is known by the 

 technical term of Conchifera. In them each valve corresponds with 

 the right or left side. 



In the first family, of which the common Oyster is a very familiar 

 instance, the two valves are unequal 

 in size, and the animal inhabits the 

 sea. The Oyster is too well known 

 to need description, but it may be men- 

 tioned that practical naturalists have for 

 some years been carefully studying its 

 habits for the purpose of breeding the 

 valuable molluscs artificially, and so of 

 securing a constant supply throughout 

 the four months of the year during OvsTERs^O^-m eduUs). 

 which the creature is out of condition. 



In this country the system is being gradually carried out, but in France 

 it is developed to a very large extent and with great success. 



The next family are termed wing-shells, or Avicularid^e, because the 

 apices — or " umbones," as they are called — are flattened and spread on 

 either side, something like the wing of a bird. The interior of the 

 valves is pearly, and the exterior layer is composed of a kind of 

 mosaic-work of five- or six-sided particles. This structure is easily 

 to be seen by means of a moderately-powerful simple lens merely by 

 holding up a scallop or other shell before the window, so as to allow 

 the light to pass through it. 



The common Scallop is found along our southern coasts and in the 

 seas of Europe. This shell was formerly used as the badge of a pilgrim 

 to the Holy Land : 



" His pilgrim's staff he bore. 

 And fix'd the Scallop in his hat before." 



It is a singular fact that in the stomach of a common Scallop is 

 found an earthy deposit which, when boiled in nitric acid in order to 

 dissolve the animal and other portions, exhibits, under a powerful 

 microscope, animalcules precisely similar to those which in a fossil state 

 form the earth on which the town of Richmond, in America, is built. 



61 * 



